Electric batteries and alloys therefor

ABSTRACT

This invention relates to electrical batteries having an anode made essentially of a magnesium base alloy containing 1 to 15 percent by weight thallium, 0 to 10 percent aluminum and to foil made of such alloy.

United States Patent 1191 King et al. March 6, 1973 1 ELECTRIC BATTERIES AND ALLOYS [56] References Cited THEREFOR UNITED STATES PATENTS [75] lnventors: John Frederick King, Manchester;

Robert Kenneth Packer, Dorset, 2,233,953 3/1941 McDonald ..75/168 B Weymouth, both of England 2,286,869 6/1942 McDonald ....75/l68 R 3,615,371 10/1971 Nakajima et al. ..75/l42 [731 Asslgne= fl' Elem" Limited 3,288,649 11/1966 McCallum ..l36/90 Manchester, Eng'and 3,432,350 3/1969 Wilson ..136/100 M 22 Filed: 6 1969 2,715,653 8/1955 Reid ....136/100 M 2,270,195 1/1942 McDonald .175/l68 pp 849,284 303,611 5/1943 Burkhardt et a1. ..75/l68 Foreign Application Priority Data Primary Examiner-Carl Quarfonh Assistant Examiner-B. Hunt Aug. 9, 1968 Great Bntam ..38, 087/68 An0mey Nohe and n [52] US. Cl. ..136/l00 M, /168 R, [57] ABSTRACT [51] Int. Cl. ..H0lm 17/02 This invention relates to electrical batteries having an [58] Field of Search ..l36/ M, 75/ 168 anode made essentially of a magnesium base alloy containing 1 to 15 percent by weight thallium, 0 to 10 percent aluminum and to foil made of such alloy.

12 Claims, 1 Drawing Figure ELECTRIC BATTERIES AND ALLOYS THEREFOR This invention relates to magnesium base alloys and to electrical cells.

The object of the invention is to provide magnesium base alloys having improved electrochemical properties when used as anodes in various electrical battery systems.

The main types of battery systems in which magnesium based alloys are used are the magnesium-sea-water cell, normally using silver chloride as the cathode, and the magnesium Leclanche type dry cell, using manganese dioxide or other materials as a depolarizer.

The magnesium based alloy currently most widely used for magnesium-seawater batteries is AZ61 containing about 6 percent aluminum, 1 percent zinc, and 0.2 percent manganese. This alloy was found to give the best compromise of properties required for the successful operation of a magnesium-seawater cell, namely high electrode potential when operating at high discharge rates, and formation of a very fine granular reaction product which is easily flushed out of the cell without causing any clogging or blockage of the cell. Solution treatment for several hours at 400C is essential to produce a uniform single phase structure giving the required properties in this alloy. Typical cell voltages for this alloy in the form of thin scratch brushed sheets when operating in a magnesium-seawater-silver chloride cell with flowing electrolyte, with flowing seawater of a salinity 21, at 20-25C, and an electrode separation of 0.020 0.023 in. at a current density of about 2 amperes per square inch are of the order of 1.0 volts.

By the addition of other elements to the above composition, other alloys have been developed which give higher electrode potentials under discharge without any significant deterioration in the form of the reaction product. Such alloys may contain typically 6 percent aluminum, 1 percent zinc, 0.2 percent manganese with up to 10 percent of lead, or 1 to 10 percent of lead, and 0.5 to 5 percent of mercury and have been described in U.S. Pat. No. 3,288,649.

One typical alloy, containing about 7 percent aluminum, 1 percent zinc, 0.2 percent manganese and 5 percent lead, was rolled to thin sheet then solution treated to produce a uniform single phase structure, and the surface was scratch brushed. When operating in a magnesium-seawater-silver chloride cell with flowing electrolyte and an electrode separation of 0.020 0.023 in. at a current density of about 2 amperes per square inch, this alloy gave average cell voltages of the order of 1.15 volts.

Pure magnesium itself is unsuitable for these applications since during the operation of the cell the reaction product formed is thick, flaky and adherent, and has the effect of polarizing the magnesium and blocking the cell. Similarly, if additions of lead or mercury are made to pure magnesium alone, the desirable combination of high potential and fine non-blocking reaction product cannot be achieved.

We have now found that if additions of thallium, within certain limits, are made to pure magnesium, alloys can be made which slow a very high electrode potential under discharge, and which do not form a thick reaction product likely to block the cell. Alloys containing thallium can be extruded or rolled to thin sheet without difficulty.

Table I shows typical electrode potential values and details of the reaction product as determined from tests in which the magnesium alloys were made the anodes in an electrical circuitso as to simulate the condition of discharge in a high energy density seawater cell. The alloys were in the form of round cast bars which had been solution treated to produce a uniform single phase structure The potential figures are volts with respect to nonpolarized AgCl and free of resistance drop across the cell.

When an alloy consisting of Mg 7% percent thallium was rolled to thin sheet and heat treated to produce a uniform structure, then used in a magnesium-seawater-silver chloride cell with flowing electrolyte and an electrode separation of 0.020 0.023 in. at a current density of about 2 amperes per square inch, cell voltages as high as 1.4 volts were recorded.

Because of the high solubility of thallium in magnesium, the likelihood of thallium forming an undesirable second phase in the metal during processing is very much reduced. Thus solution treatment of the binary alloy is necessary only to ensure an even distribution of the thallium through the material.

The electrode potential of alloys containing thallium can be increased by raising the thallium content up to 15 percent, beyond which no further benefit is obtained. This is indicated by FIG. 1 which shows the variation in maximum and average potential during a 5 minute discharge and also hydrogen evolution with thallium content. These figures were obtained from a test in which the cross-section of a cast bar was made the anode in a cell containing seawater, the other electrode being a platinum grid. Current was passed through the cell to simulate battery discharge at 2 amps/in, and electrode potentials at the magnesium surface were measured against a silver-silver chloride capillary electrode. Hydrogen from the anode was collected during the test.

For seawater battery use the optimum alloys are those giving the least sludging during discharge, which also corresponds to the least hydrogen evolution. These are the ones containing between 4 and 12 percent thallium, and particularly between 5 and percent, e.g. 6 to 9 percent.

For magnesium dry cells, and for some low drain seawater batteries, the form of the reaction product is not as critical as for seawater batteries, and consequently lower concentrations of thallium, which still give increased electrode potential, but thicker more adherent reaction products during operation, could be used.

If aluminum is added to magnesium based alloys containing thallium, a more flaky but less adherent reaction product occurs during operation. becoming increasingly fine with increasing aluminum content. Aluminum in the range 4 7 percent produces a fine flaky deposit easily washed from the surface of the plate, but with smaller additions of aluminum a thick flaky deposit tends to build up on the metal surface causing a drop in potential. I

For example, when tested under the same conditions as those in Table I, an alloy containing 7% percent thallium with 5 percent aluminum showed an electrode potential of 1.78 volts with an almost completely clean surface, and an alloy containing 11 percent thallium with 5 percent aluminum showed an electrode potential of 1.83 volts with only a loose powdery deposit on the surface. Additions of up to 10 percent of aluminum could be made to the alloys.

Table 11 gives typical voltages and sludging behavior for various alloys obtained in a single cell test rig with flowing artificial seawater. Cells 6 X 2" in dimensions were assembled by sandwiching a magnesium alloy sheet and a silver chloride sheet between silver conductors. The electrolyte gap between the magnesium and the silver chloride was maintained by glass beads embedded in the silver chloride. A separation of 0.024 ins. 35

was used with a linear electrolyte flow rate of 6 Preferred Optimum Thallium l to 15 percent by weight Aluminum 0 to 10 Mercury 0 to 5 Lead 0 to 5 Zinc 0 to 3 Manganese 0 to 1 Calcium 0 to l Cadmium 0 to l u u u The water activated battery may have a cathode chloride plate associated with silver foil or other conducting material and with an anode of the magnesium alloy in the form of thin rolled sheet of 5 to 25 (e.g. 10 to 20) thousandths of an inch thickness spaced (e.g. 20 100 thousandths inch) from the chloride.

The heat treatment of the alloys may be effected at temperatures ranging from 350 to 450C for 4 to 60 hours, e.g. 380 420C for 8 24 hours for alloys containing up to 12 percent thallium.

The alloy of the present invention contains at least 80 percent magnesium.

The invention may also be applied to an air battery an example of which is described in the specification of U.S. Pat. No. 1 140635, by making the anode in an alloy as above described. The anode may be rolled or extruded alloy e.g. about 0.05 to 0.15 inch thickness.

Alloy, percent 'lypieal voltage after stated time 1 1% 2 4 6 8 min. min. min. min. min. min. Sludging behaviour 1.17 1. 16 1.14 1.10 1.06 1.05 Black deposit on metal. 1. 20 1. 20 1.10 1.15 1.12 1.15 Slight black deposit on metal. 1. 26 1. 25 1. 2i 1. 25 1. 2 1 1.14 Do. 1. 28 1. 32 1. 41 1. 36 1. 11 0. 84 Moderately thick adherent black film. 1. 1. 37 1. all 1. 30 1. 05 0. 71 Thick black film. 1. 28 1. 20 1.31 1. 34 1. 19 1. 00 D0. 1. 30 1. 33 1. 1. 24 1. 06 1.00 Loose flaky deposit. 1. 32 1. 31 1.30 1.18 1.10 1.03 Do. 1. 33 1. 30 1. 27 1. 17 0.99 1. 02 Thick flaky deposit. 1. 33 1. 30 1. 28 1.17 1.00 1. 06 Do. 1.10 1. 10 1. O8 1. O3 0.96 0. 94 Clean surface. 1. 28 1. 27 1. 2G 1. 21 1.15 1.13 Fairly clean surface. 1. 29 1. 28 1. 27 1. 22 1. 17 1.15 D0. 1. 30 1. 28 1. 26 1. 21 1.15 1.12 Slight/powdery deposit. 1. 32 1. Z 1. 27 1. 22 1. 15 1. 10 Moderate powdery deposit. 1. 37 1. 32 1. 2.) 1.14 0. 86 0.72 Very thiek deposit. 1. 27 1. 27 1. 213 1. 21 1.17 1.16 Clean surface. 1. 22 1.22 1. 21 1.18 1.12 1.12 Do. 1. 25 1. 26 1. 26 1. 21 1.17 1.12 Moderately thick deposit.

1. 04 1. 04 1. 03 0.97 0.92 0.91 Clean surface. 1.18 1. 18 1.17 1.11 1. 05 1. 03 Slight black powdery deposit.

cms/sec. between the plates. Cells were discharged at a We claim:

constant 2 amps/in for up to 10 minutes. The electrolyte salinity was 21 and the temperature was 25C.

The addition of mercury or lead to magnesium battery alloys increases the electrode potential of the alloy. it has been found that if additions of lead and/or mercury are made to thallium containing alloys, a further increase in electrode potential can be obtained, although with a slight increase in sludging. Additions of up to 5 percent e.g. 0.5 to 5 percent of either or each element could be made. Addition of mercury to thalli- 1. An electrical battery having an anode made of a magnesium base alloy consisting of:

member employing a silver chloride or cuprous 2. A battery as claimed in claim 1 wherein the battery is of the water activated type and the anode is in the form of rolled foil having a thickness of 5 to 25 thousandths of an inch.

3. A battery as claimed in claim 2 wherein the foil is from 10 to 20 thousandths inch thick.

4. A battery as claimed in claim 1 of the air battery type.

5. A battery as claimed in claim 5 wherein the anode is the magnesium alloy in extruded form.

6. A magnesium base alloy consisting of:

Thallium 6 to 8 percent by weight Aluminum 4 to 6 percent by weight Mercury to percent by weight Lead 0 to 5 percent by weight Zinc 0 to 3 percent by weight Manganese 0 to l percent by weight Calcium 0 to 1 percent by weight Cadmium 0 to 1 percent by weight Magnesium at least 80 percent by weight and 0.5 to 5 percent total by weight of at least one of lead and mercury in the form of rolled foil having a thickness of 10 to 20 thousandths of an inch.

7. A battery as claimed in claim 1 wherein the alloy contains 4 to 10 percent thallium and l to 7 percent aluminum.

8. A battery as claimed in claim 1 wherein the alloy contains 6 to 8 percent thallium and 4 to 6 percent aluminum.

9. A battery as claimed in claim 1 wherein the alloy contains 6 to 8 percent thallium, 4 to 6 percent aluminum, and 0.5 to 5 percent total of at least one of lead and mercury.

10. The product of the process of heat treating at 350 to 450C for 4 to 60 hours a magnesium base alloy consisting of:

Thallium 6 to 8 percent by weight Aluminum 4 to 6 percent by weight Mercury 0 to 5 percent by weight Lead 0 to 5 percent by weight Zinc 0 to 3 percent by weight Manganese 0 to 1 percent by weight Calcium 0 to 1 percent by weight Cadmium O to 1 percent by weight Thallium 6 to 8 percent by weight Aluminum 4 to 6 percent by weight Mercury 0 to 5 percent by weight Lead 0 to 5 percent by weight Zinc 0 to 3 percent by weight Manganese 0 to 1 percent by weight Calcium 0 to 1 percent by weight Cadmium 0 to 1 percent by weight Magnesium at least percent by weight and at least 0.5 percent total by weight of at least one of lead and mercury. 

1. An electrical battery having an anode made of a magnesium base alloy consisting of: Thallium 1 to 15 percent by weight Aluminum 0 to 10 percent by weight Mercury 0 to 5 percent by weight Lead 0 to 5 percent by weight Zinc 0 to 3 percent by weight Manganese 0 to 1 percent by weight Calcium 0 to 1 percent by weight Cadmium 0 to 1 percent by weight Magnesium at least 80% by weight.
 2. A battery as claimed in claim 1 wherein the battery is of the water activated type and the anode is in the form of rolled foil having a thickness of 5 to 25 thousandths of an inch.
 3. A battery as claimed in claim 2 wherein the foil is from 10 to 20 thousandths inch thick.
 4. A battery as claimed in claim 1 of the ''''air battery'''' type.
 5. A battery as claimed in claim 5 wherein the anode is the magnesium alloy in extruded form.
 6. A magnesium base alloy consisting of: Thallium 6 to 8 percent by weight Aluminum 4 to 6 percent by weight Mercury 0 to 5 percent by weight Lead 0 to 5 percent by weight Zinc 0 to 3 percent by weight Manganese 0 to 1 percent by weight Calcium 0 to 1 percent by weight Cadmium 0 to 1 percent by weight Magnesium at least 80 percent by weight and 0.5 to 5 percent total by weight of at least one of lead and mercury in the form of rolled foil having a thickness of 10 to 20 thousandths of an inch.
 7. A battery as claimed in claim 1 wherein the alloy contains 4 to 10 percent thallium and 1 to 7 percent aluminum.
 8. A battery as claimed in claim 1 wherein the alloy contains 6 to 8 percent thallium and 4 to 6 percent aluminum.
 9. A battery as claimed in claim 1 wherein the alloy contains 6 to 8 percent thallium, 4 to 6 percent aluminum, and 0.5 to 5 percent total of at least one of lead and mercury.
 10. The product of the process of heat treating at 350* to 450*C for 4 to 60 hours a magnesium base alloy consisting of: Thallium 6 to 8 percent by weight Aluminum 4 to 6 percent by weight Mercury 0 to 5 percent by weight Lead 0 to 5 percent by weight Zinc 0 to 3 percent by weight Manganese 0 to 1 percent by weight Calcium 0 to 1 percent by weight Cadmium 0 to 1 percent by weight Magnesium at least 80 percent by weight and 0.5 to 5 percent total by weight of at least one of lead and mercury in the form of rolled foil having a thickness of 10 to 20 thousandths of an inch.
 11. A battery as claimed in claim 1, further comprising housing means, said housing means containing said anode. 